1. Field of the Invention
The present invention relates to an optical recording medium and in particular to an optical recording medium of a heat mode type which comprises a novel dye or further a quencher and on which information may be recorded and reproduced by irradiating with a laser beam.
2. Description of the Prior Art
Heretofore, there has been known an information recording medium which makes it possible to record and reproduce information by irradiating a disk-like information recording medium, which is rotating, with a laser beam. As an example of such a recording medium, those of the pit-formation type are well known. In such a pit type optical recording medium of heat mode, a light for recording is utilized as a heat source for forming pits. For example, the recording of information is effected by melting and removing a part of the recording medium while irradiating the medium with light for recording such as a laser beam to form pits thereon and on the other hand, the readout of the information recorded as such pits is effected by detecting these pits while scanning the medium with light for readout.
As a recording layer for such a recording medium, the use of low melting metals or a combination of a low melting metal and a dielectric material such as a resin have conventionally been proposed. However, they suffer a lot of disadvantages such taht they are inferior in storability, they have a low resolution, they have a low recording density and they are less economical.
Recently, it has been proposed to use a dye film as a recording layer, which causes changes in physical properties by irradiating it with light having a rather long wave length and it has already been put into practical use. This kind of dye film in general comprises a variety of dyes or a combination of a dye and a resin. However, these dye films also have problems to be solved such that if this kind of optical recording medium is subjected to repeated erasing operations or repeated irradiation with light for readout or is stored for a long period of time, the sensitivity and the C/N ratio therefore and remarkably reduced.
Under such circumstances, in order to improve the dye in the stability to light and in particular to prevent the decoloration (deterioration during reproduction) thereof owing to the light for readout, it has been proposed to use a dye and a quencher in combination. In this respect, reference is made to, for instance, Japanese Patent Unexamined Published Application Nos. 60-162691; 60-201988; 60-203488 and 60-257290.
However, even if a quencher is used in combination, an optical recording medium having a good resistance to light for readout and/or stability to long term storage has not yet been obtained, in other words, it has not yet been acceptable practically.